The high-temperature storage units which can be used in conjunction with a power station arrangement, among which are to be counted especially metal oxide storage units (rechargeable metal oxide battery, ROB), including especially metal oxide-air storage units (the metal-air storage units are equivalent), require increased operating temperatures during normal operation and consequently require an at least time-based supply with thermal energy. Above all, in the case of metal oxide-air storage units operating temperatures of over 600° C. are sometimes necessary in order to be able to ensure the necessary ion fluxes in the storage unit in a sufficiently loss-free manner. Since the charging process in the case of such storage units procedes endothermically, moreover, cooling takes place during the charging which can only be reduced or prevented by sufficient heat being fed to the storage unit. Also, during a stationary operation, cooling is carried out mainly by heat losses which need to be compensated. In contrast to this, high-temperature storage units, however, during the discharging process release thermal energy which is generated during exothermic discharging processes and consequently has to be dissipated.
Here, and in which follows, the invention shall relate to high-temperature storage units which are designed for storing and releasing electric power station capacity. Therefore, these are especially electrochemical high-temperature storage units, such as metal oxide storage units.
Further high-temperature storage units are NaNiCl storage units or NaS storage units which have to be operated at temperatures of at least 200° C. Metal oxide storage units, especially metal oxide-air storage units, typically have an operating temperature of up to 900° C. and more so that in the present case the high-temperature storage units are distinguished by an operating temperature of approximately at least 200° C. to about 900° C. The high-temperature storage units according to the invention are distinguished by the fact that they are designed for receiving electric energy (electric current) and for converting it for example by electrochemical reactions into a suitable chemical storage product and for storing it. Such a storage unit is also in a position, however, when necessary, to provide electric energy (electric current) again by means of an electrochemical reverse reaction of this storage product, for example.
Especially the metal oxide-air storage unit developed by the applicant, which is described in more detail for example in DE 10 2009 057 720, requires an at least time-based supply with thermal energy at a temperature level of between 500° C. and 850° C. According to the internally known prior art, this heat can be provided via the air which is fed to the storage unit as process gas. The air is thermally conditioned in this case by means of an electric heating device before it is fed to the storage unit. Alternatively to this, or in addition, heating elements can also be provided inside the metal oxide-air storage unit and can supply the storage unit with thermal energy during operation.
As a further alternative, a high-temperature storage unit can also be operated with increased charging voltage during the charging process, as a result of which the charging current density of the storage unit is increased. As a consequence of increasing this charging current density, the ohmic power loss also increases during the charging process, which can in turn be partially made available to the storage unit as waste heat output.
A disadvantage to the previously described method for heat supply of a high-temperature storage unit is on the one hand that the provision of the thermal output can be achieved only by expenditure of additional energy and therefore by incurring additional costs. On the other hand, the high-temperature storage units are sometimes also to be constructionally adapted so that a suitable heat supply can be enabled in the first place. A heat supply by means of suitable heating elements integrated into the storage unit especially necessitates a high constructional cost.
An external supply of a high-temperature battery with thermal energy is described in the post-published printed document DE 10 2012 203 665 A1. In this, it is instructed to extract thermal energy from the exhaust gas flow of a gas turbine by means of a heat exchanger which is located in this exhaust gas flow. The thermal energy in this case is transferred to a fluid which is fed to the high-temperature battery and can therefore also provide the thermal energy.
An alternative external supply of a solid oxide fuel cell, which can also be operated in the reverse direction for storing hydrogen as fuel, is described in the prior-publicized printed document JP03208259A. In this case, it is instructed that steam from a nuclear power-station steam generator after additional superheating can be fed to the fuel cell for the transfer of heat.
A disadvantage of these solutions known from the prior art, however, is that the thermal energy which is fed to the high-temperature battery or to the solid oxide fuel cell sometimes does not allow sufficiently advantageous energetic utilization of the primary heat source. Whereas in DE102012203665 A1 it is instructed to extract the thermal energy directly from the exhaust gas flow of a gas turbine and to therefore disadvantageously cool this for further applications, JP03208259A instructs a direct fluidic connection to a water-steam cycle of a nuclear power station.
When supplying a high-temperature storage unit by means of an increased waste heat output in the case of increased charging current density, however, a chemical or even physical degradation of the storage unit is sometimes to be feared. Moreover, during the charging process under increased charging output the charging current density is typically significantly higher in comparison to the discharging current density, which in turn requires a suitable adaptation and dimensioning of the associated electrical infrastructure